What Causes Depression? What You Believe Matters

Hans Schroder, Ph.D., contributed to this post.

Those who have experienced depression often ask themselves, “Where did this come from?” This is an old question — a very old question. Societal views on the origins of mental illness have changed considerably over the course of history.

During ancient times, for instance, it was popular to believe that demonic possessions were responsible for the onset of psychological illness. This viewpoint shifted considerably when Hippocrates, in Ancient Greece, posited that an imbalance in bodily humors (black bile, yellow bile, phlegm, and blood) was at the heart of mental illness. At the time, this was considered a major scientific and medical breakthrough, and the humoral theory was well-embraced by the medical community for over 2,000 years.

Fast-forward to the 20th century, when Freudian theories suggested unconscious conflicts and unresolved traumatic experiences gave rise to mental disturbances, and then later cognitive-behavioral theorists suggest that maladaptive beliefs were at the core of most illnesses.

As detailed in a recent book by Anne Harrington (Mind Fixers), the last 50 years have seen a substantial rise in another set of explanations of mental illness, this time focusing on neurobiological, chemical, and genetic contributions. The so-called “chemical imbalance theory” of depression suggests that an imbalance in neurotransmitters such as serotonin — chemical messengers between nerve cells — is the reason why people are depressed.

While no longer really a theory in the technical sense — it is certainly not so simple as a deficiency in serotonin that can explain depression — this narrative remains popular. The chemical imbalance message has been promoted by many well-intentioned stakeholders, including pharmaceutical companies, anti-stigma groups, and mental health professionals. An antidepressant’s television commercial that aired in 2001 and was seen by millions claimed that “while the cause is unknown, depression may be related to an imbalance of natural chemicals between nerve cells in the brain.”

Until a few months ago, a Google search for “clinical depression” returned an image of a brain with the phrase “abnormalities in neural circuits may be a cause.” Clearly, this emphasis on biological and chemical origins of mental illness is prevalent.

There is something powerful about ascribing personality traits, psychological distress, and our behaviors to biochemical and genetic origins. First, these explanations can seem to provide validation to people who have not had an explanation for their depression. When people view their depression as a real, medical illness with a biochemical cause, this often brings relief; not only is there a name for what they are experiencing, it is a diagnosable medical phenomenon.

A second reason the biochemical narrative is powerful is that it can take away blame from individuals who experience depression. Depression is often associated with feelings of blame, and many people also blame themselves for being depressed in the first place. The chemical imbalance idea takes away this aspect of self-blame completely by placing fault with brain chemicals.           

Third, the biochemical narrative is intuitive for encouraging treatment-seeking behavior. If depression is caused by a chemical imbalance, then a medication correcting this imbalance would seem to be helpful.

Despite these potential positives of this narrative, emerging research indicates several downsides of emphasizing biological and genetic contributions to psychological distress:

• When people are exposed to genetic feedback that they have a predisposition to depression, they tend to feel they are powerless over this experience and may think that their depression will last longer (Lebowitz & Appelbaum, 2019).
• These messages inherently imply that medications are more effective than other treatments, which, in the case of depression, is not true. This may bias individuals away from helpful therapies such as talk therapy.
• Biogenetic messages actually increase stigmatizing attitudes in other domains. People perceive those with mental illness as more dangerous if they are told that mental illness is genetic (Haslam & Kvaale, 2015).
• Biogenetic messages may decrease hope for recovery. If something is said to be chemical or genetic, it is often assumed that this cannot change.

Holding onto hope is a critical aspect to recovery, especially for those with depression, who often experience a sense of hopelessness. I have heard multiple patients tell me that their depression and anxiety “feels so chemical.” These sentiments are often followed by feelings of discouragement and hopelessness, especially when it comes to learning new behavioral skills and thinking strategies to help combat anxiety and depression. So, while biological messages may reduce self-blame, there seems to be a darker side to attributing depression solely to biogenetic origins.

We recently examined how beliefs about the causes of depression relate to treatment expectations and outcomes in the Behavioral Health Partial Hospital Program at McLean Hospital (Schroder et al., 2020). We asked 279 people attending our clinic to complete several surveys before and after they took part in treatment. The treatment was intensive and included attending several group therapy sessions per day, learning new behavioral and thinking strategies, several individual therapy sessions per week, and medication management. Overall, the program emphasized learning behavioral skills that people can use to help regulate their emotions, better cope with symptoms, and improve their functioning and well-being.

Here’s what we found:

• Patients who strongly endorsed a chemical imbalance belief about depression at the start of the program expected less out of it, especially if they had more severe symptoms of depression. This finding extends previous research using thought experiments in which college students had lower expectations for psychotherapy if they were given a fake saliva test and told they had a chemical imbalance (Kemp et al., 2014). 
• Chemical imbalance beliefs at the start of treatment predicted more depressive symptoms at the end of it. In that statistical analysis, we also controlled for previous depressive symptoms, other psychiatric symptoms, inpatient psychiatric hospitalization history, and treatment expectations. 

Overall, our findings fit with the emerging research highlighting the downsides of emphasizing solely biogenetic explanations of mental illness. While our study was correlational and not experimental, meaning we cannot say that chemical imbalance beliefs caused poorer expectations and treatment outcomes, they are certainly suggestive and fit with other studies that did use experimental designs.

Going forward, researchers, clinicians, and the public should reconsider the emphasis on biology and genetics as the primary causal agents in mental distress. Although they are more complex, biopsychosocial models of emotional disorders may better capture the multiple influences on mental health. Biopsychosocial models emphasize the interaction of biology (e.g., genes), psychology (e.g., early learning, behavioral patterns), and social factors (e.g., relationships, culture) in determining one’s mental health.

As clinicians, we want to help our patients feel better. We can be pulled to say things in order to reduce their self-blame, and it can sometimes feel like a knee-jerk reaction to discuss the purported scientific literature and invoke biogenetic narratives (e.g., “it’s a chemical imbalance, it’s not your fault”). It’s important to realize that other potential contributors to mental health (e.g., early childhood experiences and learning and societal problems such as poverty or racism) are also not the patient’s fault and may be just as important as their genes.

Our findings indicate that caution is necessary when considering invoking biological and chemical explanations. It is crucial to communicate that depression is influenced by biological, psychological, and cultural factors — and that our biology is influenced by our behavior and vice versa. There are many effective treatments for depression, and reason to be hopeful if people can keep an open mind about their prognosis.

Hans Schroder, Ph.D., is a Clinical Lecturer and Postdoctoral Fellow in the Department of Psychiatry, and Postdoctoral Fellow in the Center for Bioethics and Social Sciences in Medicine at the University of Michigan.